This invention relates, in general, to a method for forming a passivation layer on a conductive layer, and more particularly, to a method for forming a dielectric layer on a high temperature metal layer.
Integrated circuit contacts and interconnects often comprise, among other things, heavily doped polysilicon. However, because the sheet resistance of heavily doped polysilicon films is on the order of 20 ohms/square, these films cause long RC time constants and hence, undesirable time delays. This undesirable time delay negatively impacts the ability to fabricate dense, high performance semiconductor devices. As a result, several methods have been used to improve the sheet resistance of semiconductor interconnects.
One method is the polycide method where a metal silicide is formed over a doped polysilicon layer. This method has a disadvantage in that it requires depositing and patterning two films. Also, when the metal silicide layer is formed over the polysilicon, the silicide formation tends to deplete dopants in the polysilicon layer thus increasing the sheet resistance of the polysilicon layer.
It would be desirable to use a high temperature metal layer, such as titanium, vanadium, chromium, tantalum, or their nitrides, as a buried layer or as a interconnect because only one film would have to be deposited and patterned. In addition, the high temperature metal layer would provide a low sheet resistance and would not be susceptible to the dopant depletion problem found in the polycide process. However, when a patterned high temperature metal layer is used, for example, as a buried interconnect with a dielectric layer formed over the high temperature metal layer, delamination occurs between the metal layer and the dielectric layer. This is particularly true if the layers are subsequently exposed to high temperatures. This delamination problem can result in electronic component reliability problems.
Thus, there exists a need for a method for forming a dielectric layer on a high temperature metal that provides good adhesion between the dielectric layer and the high temperature metal layer.